Air Tightness Testing Process: Step-by-Step Guide

The Air Tightness Testing Process: Step-by-Step Guide

If you’re building or converting a property in the UK, you may be legally required to carry out air tightness testing to comply with Building Regulations Part L. This test plays a vital role in measuring how energy-efficient your building is by checking for unwanted air leakage. In this article, we explain the Step-by-Step process.

🏠 Why Is Air Tightness Testing Important?

Air tightness testing—also known as a blower door test—is used to measure the amount of uncontrolled air leakage from a building. It plays a critical role in:

Meeting Building Regulations Part L
Improving energy efficiency
Complying with SAP Calculations
Achieving a strong EPC rating

At Assessment Hive, we help homeowners, developers, and contractors across the UK complete this essential step with confidence. Below, we break down what to expect during the air tightness testing process, from start to finish.

✅ Step-by-Step: The Air Tightness Testing Process

Step 1: Initial Preparation

Before we arrive on site, ensure:

All external doors and windows are installed and closable
Skirting boards, sockets, pipework, and service penetrations are sealed
Loft hatches are installed and closed
Wet trades (like plastering or screeding) are completed and dry

🔗 Read: How to Prepare for an Air Tightness Test

Step 2: Installing the Blower Door Equipment

Our qualified technician will:

Fit a temporary blower door fan into an external doorway using an airtight frame and canvas
Set up a manometer (pressure gauge) to measure airflow
Connect monitoring equipment to record pressure differentials

This setup allows us to create a controlled environment to test air leakage.

Step 3: Pressurising the Building

We will use the fan to pressurise and depressurise the building (usually to 50 Pascals), simulating the effects of wind pressure on the building envelope.

We measure:

The volume of air leaking through the building fabric
The air permeability rate (measured in m³/h·m² at 50 Pa)

This value is critical for your SAP Calculation and compliance with Part L of the Building Regulations.

Step 4: Detecting Air Leaks (If Needed)

If you’re not achieving the desired result, we can assist in identifying leakage points using:

Smoke pencils
Thermal imaging
Visual inspection

Common leakage areas include:

Around windows and doors
Floor and wall junctions
Behind kitchen units or bath panels
Loft hatches and pipe penetrations

🛠️ We can advise on remedial measures to help you pass retesting if needed.

Step 5: Calculating the Result

Once the test is complete, we calculate:

The air permeability result in m³/h·m²
Whether the result meets the target set in your SAP assessment

If you meet or exceed the target — great! If not, we’ll discuss next steps.

Step 6: Issuing the Certificate

We provide:

A test certificate (valid for Building Control)
A digital report with detailed results
Same-day turnaround in most cases

You’ll need this certificate for your Energy Performance Certificate and final SAP Report.

💡 Top Tips for Passing First Time

Engage your SAP assessor early in the design process
Prioritise quality sealing around service penetrations
Use airtight membranes and quality installation techniques
Book a pre-test inspection if you’re unsure

→ Contact us for advice or to arrange your test.

🔧 Need a Fast, Professional Air Test?

At Assessment Hive, we make the Air Tightness Test process straightforward. Our team works with homeowners, architects, and builders nationwide to provide quick, accurate assessments and practical advice to achieve compliance.

Fast turnaround
Competitive pricing
Remote, nationwide service